Has done an upgrade to the vibe 90 tail case (3D version...v9)? I've heard that there can be issues with cracking case, vibrations etc. so I thought I'd go ahead and upgrade. After doing some searching I'm finding that there is not a direct upgrade for the 3D.

I've heard of people using a vibe 50 tail case and maybe someone using a trex 700 tail case...any truth to this? If so, are there modifications that are needed to work with the 90 3D?

This is what I've heard too. Someone said, I think, that there isn't much modification needed. If I recall, all I needed to do was to use the JR spline that they sell...maybe it needs to be turned, fit...don't exactly remember.